The present invention relates to an improved method and apparatus for mixing blood or another body fluid with appropriate reagents in an automatic chemistry-analyzing system, and, more particularly, to such methods and apparatus using piezoelectric phenomena.
The chemical analysis of blood or other body fluids is a vital part of medical diagnosis. Testing for various serum constituents, such as sugar or albumin, for example, or for some other medically significant factor, is generally performed in a manual or automated process by adding specific amounts of various reactive chemicals or reagents to a sample of the serum in a specific sequence and under specified conditions of temperature and time. The light transmittance value of the resulting test chemistry is then measured, and this value can be used to determine the amount of the particular constituent being measured in the serum.
More specifically, in analyzing a serum specimen, a sample of the specimen is typically placed in a test tube or other appropriate container; and one or more specific reagents are added depending on the particular test to be performed. In some cases, the reagents can all be added at once; while in others, an incubation period must take place between the addition of the required reagents. When the required chemical reactions have taken place, a sample of the completed test chemistry is removed from the test tube; and the light transmittance value of the test chemistry is ascertained using a spectrophotometer or the like. This value can be used to calculate the optical density of the chemistry from which the percentage concentration in the serum of the constituent of interest can be ascertained.
A significant portion of the analyses currently conducted on body fluids is now done automatically, and one appropriate automated system is described in detail in U.S. Pat. No. 3,901,656 which is assigned to the same assignee as the present application.
Whether done manually or by an automated system, it is important that the partially completed test chemistries be properly mixed after the addition of each reagent to assure a homogeneous mixture and fully completed reactions that will not give an erroneous result when the chemistries are analyzed. In the system described in the above-mentioned U.S. Pat. No. 3,901,656, mixing is accomplished by positioning a mixing apparatus adjacent to the reagent-dispensing heads which can be extended into the serum-reagent mixture in the test tube. This mixing apparatus comprises a mixing blade coupled to the shaft of a mixer motor which, when actuated, rapidly rotates the mixing blade to combine the mixture and uniformly distributes the reagents throughout.
There are a number of inadequacies in using such a mixing apparatus. For one thing, as is typical in motor mixers, the mixing blade is driven into a rotational motion; and this tends to form a vortex in the liquid being mixed which can pull air bubbles down into the liquid. This is undesirable as the presence of air bubbles can affect the light transmittance value of the test chemistry and give an erroneous result when the chemistries are analyzed. Also, motor mixers sometimes tend to cause foaming on the surface of the liquid which can cause the liquid to spill over the top of the test tube and contaminate other specimens within the system. In addition, in a motor mixer, there is always the possibility of mechanical breakdown as may be caused by broken belts, failed bearings, or the like; and frequently, unacceptable amounts of noise and heat are generated.